Granulocyte colony-stimulating factors, for example, recombinant granulocyte colony-stimulating factors (rG-CSF), have been known primarily as humoral factors to stimulate the differentiation and proliferation of granulocyte cells, and it has been reported in an experiment upon mice in vivo that the administration of rG-CSF enhances the hematopoiesis of the bone marrow and in addition causes remarkable extramedullary hematopoiesis in the spleen to proliferate hematopoietic stem cells and all hematopoietic precursor cells in the spleen. And it has been thought as extramedullary hematopoietic mechanism in the spleen that hematopoiesis occurs due to a splenic hematopoietic microenvironment modifications according to the stimulation of rG-CSF to enhance hematopoietic potential.
Hence, the present inventors have noted splenic stromal cells administered rG-CSF with a view to clarifying the hematopoietic potential in the spleen, and established a hematopoietic stromal cell line (CF-1 cells) from the spleen of a mouse administered rG-CSF with a view to attempting the analysis of the enhancement of the hematopoietic potential by stromal cells with rG-CSF, and examined the potential effect on hematopoiesis using the hematopoietic stromal cells, and as a result, colony-stimulating activities in vitro and potency supportive of hematopoietic stem cells in vivo have been recognized [Blood, 80, 1914 (1992)].
However, though some of splenic stromal cells have been established as a cell line (CF-1 cells), and cytological characteristics thereof have been examined, no specific antibody recognizing surface antigens thereof has been prepared so far, and characteristics thereof have been scarcely known yet.
Hence, the present inventors have engaged in assiduous studies with a view to developing specific antibodies capable of recognizing splenic stromal cells on the basis of the above information upon splenic stromal cells and the results of the studies, and prepared monoclonal antibodies using the splenic stromal cell lines as antigens for immunization, and as a result, novel monoclonal antibodies unreported so far have been obtained.
And as a result of examining the properties of the obtained monoclonal antibodies, the inventors have found surprisingly that they have the property of causing apoptosis on myeloid cells, which has led to the completion of the present invention.